1. Field of Invention
This invention relates to the light emitting region of a semiconductor light emitting device.
2. Description of Related Art
Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, a light emitting or active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. III-nitride devices formed on conductive substrates may have the p- and n-contacts formed on opposite sides of the device. Often, III-nitride devices are fabricated on insulating substrates, such as sapphire, with both contacts on the same side of the device. Such devices are mounted so light is extracted either through the contacts (known as an epitaxy-up device) or through a surface of the device opposite the contacts (known as a flip chip device).
U.S. Pat. No. 5,747,832 teaches a “light emitting gallium nitride-based compound semiconductor device of a double-heterostructure. The double-heterostructure includes a light-emitting layer formed of a low-resistivity InxGa1-xN(0<x<1) compound semiconductor doped with p-type and/or n-type impurity.” See U.S. Pat. No. 5,747,832, abstract. Specifically, column 5 lines 45-50 recite “[i]n the present invention, the light-emitting layer 18 preferably has a thickness within a range such that the light-emitting device of the present invention provides a practical relative light intensity of 90% or more. In more detail, the light-emitting layer 18 preferably has a thickness of 10 Å to 0.5 μm, and more preferably 0.01 to 0.2 μm.” Column 10 lines 44-49 teach “[i]n the third embodiment, the n-type impurity doped in InxGa1-xN of the light-emitting layer 18 is preferably silicon (Si). The concentration of the n-type impurity is preferably 1×1017/cm3 to 1×1021/cm3 from the viewpoint of the light emission characteristics, and more preferably 1×1018/cm3 to 1×1020/cm3.”
Commercial III-nitride devices with InGaN light emitting layers often have multiple quantum well light emitting layers less than 50 Å and typically doped to less than about 1×1018 cm−3, as these quantum well designs can improve performance, especially in poor quality epitaxial material, at low drive current. At higher drive currents desirable for lighting, these devices suffer decreasing efficiency with increasing current density. Needed in the art are devices that exhibit high efficiency at high current density.